1. Field of the Invention
This invention relates to a process for preparing polyimines. More particularly, it relates to a process for preparing polyimines having a high molecular weight using a phenolic compound as a reaction medium.
2. Description of the Prior Art
Since 1950 many researches have been done on polyimines having a plurality of the imine group (--CH.dbd.N--) in their main chain of the molecule from the viewpoint of its high bond energy and its possibility of ekaconjugation of double bond chemically formed with an appropriate atomic group. Especially, the characteristics of the imine group such as the resistance to heat, the semiconduction, the photoconduction, the photodielectric character and the insulation have been noted and studied. Also, various methods of preparing polyimines have been proposed. For example, Polymer Letters, 2, 943 (1964) describes a preparation of the polyimine having azulene groups in its main chain of the molecule using dimethylformamide as a solvent at the reaction temperature of 100.degree. C., but the polyimine is only an oligomer. According to Journal of Polymer Science, (Part A-1), 5, 1659 (1967) various polyimines are prepared by using, as a solvent, dimethyl sulfoxide, N-methylpyrrolidone or acetic acid, but the molecular weight of these polyimines are low and at most 3,000. Journal of Macromolecular Science (Reviews of Macromolecular Chemistry), C(3)1, 105 (1969) describes a preparation of various polyimines by a solution polymerization method using, as a solvent, an alcohol and acetic acid, a melting method and an azeotropic method using, as a solvent, benzene. Japanese Patent Application (OPI) No. 138800/1976 describes a method of preparing fibers and films from polyimines having a low melting point in the liquid crystal state and Belgian Patent No. 622,556 describes a preparation of polyimines having aliphatic chains in the molecule using, as a solvent, benzene.
However, according to these methods it is hardly possible to produce high molecular weight polyimines, and even if high molecular weight polyimines are obtained, their processability or moldability are low.